This invention relates to a development in the art of xerography wherein a light and shadow image pattern is developed by passing a liquid ink developer from a dispensing member to an image surface. More particularly, this invention relates to a method for fabricating an improved fluid dispensing sleeve member used for developing or making visible electrostatic images, and further relates to the fluid dispensing sleeve member so fabricated.
In general, the art of xerography is characterized by the formation of an electrostatic image corresponding to the image desired to be reproduced. That image is then developed or made visible by the deposition of electrostatically attractable material onto any suitable surface. In conventional xerographic applications, the electrostatically attractable material is usually a finely divided insulating powder, though in recent years fluid developers such as liquid ink have been the subject of considerable experimentation. The general technique for the fluid development of electrostatic images is well-known, and is described in detail by R. W. Gundlach in U.S. Pat. No. 3,084,043.
Essential to such liquid development techniques is a fluid dispensing sleeve member adapted to receive a quantity of fluid developer, such as electrically charged ink, from conventional applicator means. The dispensing member must be adapted to hold the ink in a stable manner until it is subjected to the attractive forces of an electrostatic image, whereupon the ink is dispensed in conformity with that image. To properly receive and hold ink in this manner, it has been found that the outer surface of the preferably cylindrical dispensing member should have a microscopic pattern of closely spaced grooves, embossments or recesses, sometimes referred to herein as pockets. These pockets are adapted to hold minute quantities of ink by capillary attraction. It has been also found that the outside surface of the dispensing member should be comprised of flexible or elastomeric material to reduce, for example, the possibility of damaging the microscopic pattern when the dispensing member is brought into contact with ink applicator means. Other desirable qualities of the dispensing member include a rigidity or stiffener component which enables the member to maintain its shape, and electrical conductivity properties which enable the member to hold a charge. This latter quality is necessary, notwithstanding the effects of capillary attraction, to maintain ink in the microscopic pockets until pulled away by the electrostatic forces corresponding to the image to be reproduced.
The demanding requirements of the dispensing member have, heretofore, made fabrication both difficult and expensive. For example, the dispensing member does not readily lend itself to fabrication from a full cylindrical mold because the microscopic recesses and embossments thereof interlace with those of the completed member, thereby making it difficult to remove the dispensing member from the mold without damaging the delicately patterned surface. Though a shell or split mold would avoid some of these problems, such a mold suffers from the drawback that it leaves undesirable seams or parting lines on the outer surface of the completed dispensing member. Moreover, dispensing members fabricated from conventional molds are often pockmarked with air bubbles trapped inside the mold. As a result of these and other deficiencies, some efforts have been made to avoid using a mold and instead to try embossing a resilient cylinder. This method of fabrication is impractical, however, because it is laborious and very uneconomical.
Another fabrication problem results, not from the particular method employed, but the type of materials required. More specifically, the seemingly contradictory requirements that the completed member be resilient, rigid and electrically conductive tend to compromise the finished product. Due to these and other problems in designing and fabricating a dispensing member of the type required, liquid development of electrostatic images has remained a promising but impractical xerographic application.